Ubuntu Server25.10 : SSH connection with authentication using public key cryptography

SSH connection using authentication with public-key cryptography

 Creation of public and private key pairs

Create a public/private key pair for a user connecting to the Linux server using OpenSSH.
Use ssh-keygen to create key pairs.
This time, we will create a key set using the RSA cipher used in the SSH protocol Version 2.
Creation of public/private key pairs is performed with remote login user privileges (huong).
If you do not specify the destination and file name, id_ed25519,id_ed25519.pub will be created in /home/huong/.ssh/. On the way, enter the password for the key.

Save the generated private key id_ed25519 to the Windows directory c:\USERS\user\.ssh\ using winSCP
Start Winscp
Host name  : Server IP Address
Port number : SSH Port
User name : Server Login User
Password : Password for the same user
and then "Save".

Site name : Any name
Click "OK"

After confirming the server, click "Login".

Click "Update" when the following screen appears

Password of the logged-in user in the Password field

Once connected, the left pane shows the server side, and the right pane shows the PC (Windows) side.
Copy the "id_ed25519" file located in the .ssh directory to the Windows directory[c:\USERS\user\.ssh] on the right side.

Editing SSH Configuration File

Edit the SSH configuration file to disable password authentication.
This time, instead of being an ordinary user, su - to become root.

How to connect using Tabby Terminal
Specify the key using the option [-i c:\USERS\xxxxx\.ssh\id_ed25519]

Creating a private key using PuTTYgen

Start Winscp and launch [Run Puttygen] from [Tools].
Select the appropriate server

Click Load

The [ Open File Dialog ] will open, change the file type to [ All Files (*. Change the file type to [ All Files (*. *) ] and load the private key id_ed25519 that was transferred from the Linux server.

The password is the password set in "Creating a public and private key pair" above

Click on "Save private key"

Save the file with the extension ".ppk" in the same place as "id_ed25519" saved earlier on the Windows side under the name "id_ed25519.ppk".

Select the target server and click "Edit".

Click on "Advanced"

Open the "Authentication" menu and specify "id_ed25519.ppk" saved in Windows for "Private key file

Click "Save"

Click on "Login"

The password is the password set in "Creating a public and private key pair" above

When connecting via Tabby Terminal, do the following:

If you encounter an error like the one below, convert your private key to OpenSSH format.

Launch [WinSCP] > [Run PuTTygen], then import the private key under [Import key] in the [Conversions] tab.

Convert the imported private key to OpenSSH format and save it under a different name
The password specified when creating the public key

Using the [id_ed25519_2.ppk] file converted to OpenSSH format, you can connect as follows: